Interesting question and observation. I think part of it depends on the size of your control panel (and total controls) along with the specific games you want to support.
Something like Arkanoid for instance doesn't matter that much if the spinner is favoring the left or right, although some may prefer it be centered with the screen like the original. Some of it depends if you're goal is to support left handed vs right handed preferences. However other games that use spinners in tandem with other controls, like Tron, seem to suggest the spinner should be on the left relative to where ever your flight stick is mounted. I can't imagine playing Tron with opposite hands. However it's funny because fighting games and many others force you to use your left hand for directional controls. Why Tron went the opposite is interesting, but given it's a flight stick I would say I've always naturally flown with my dominant hand (right). Maybe all the fighting games got it wrong and we should be controlling direction with our dominant hands?
Similarly with a game like Pacman where you only have a joystick, I always found myself using my dominant hand there too.
From what I can think of Tron maybe a more unique scenario putting the spinner on the left. If Tron isn't your thing, then it may just come down to what buttons you have available to the left or right side of it and your hand preference. In looking at some older CPs, like tempest for instance, they forced you to use your right hand on the spinner and really spaced out your 2 buttons, which from a user input standpoint wasn't the most efficient layout. I guess they wanted to make sure you were really deliberate about using your super zapper.
Out of curiosity I pulled up a quick list of common spinner games (not counting driving or rotary stick) from an older post I found on here to see which placement was more dominant. There were more Tron layout clones than I thought.
Center - Arkanoid (World) arkanoid (spinner + buttons)
Center - Arkanoid - Revenge of DOH (World) arknoid2 (spinner + buttons)
Left - Blasteroids (version 4) blstroid (spinner + buttons)
Right - Tempest (rev 3) tempest (spinner + buttons)
Left - Tron (set 1) tron (spinner + flight stick)
Left - Mad Planets mplanets (spinner + flight stick)
Center - 720 Degrees (set 1) 720 (spinner + buttons)
Left - Aztarac aztarac (spinner + flight stick)
Right - Forgotten Worlds (US) forgottn (spinner + joystick) (defies Tron control layout!)
Left - Kozmik Kroozr kroozr (spihner + flight stick)
Left - Crater Raider crater (spinner + flight stick)
Center - Wheel Of Fortune wfortune (spinner + buttons)
Center to each player - Two Tigers twotiger (spinner + buttons)
Up/Down Spinner
Left - Discs of Tron (Upright) dotron (spinner + flight stick)
Left - Zwackery zwackery (spinner + flight stick)
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Total Games In List: 15
Total Centered: 5 (33%)
Total Left: 8 (54%)
Total Right: 2 (13%)